1. Technical Field
The present invention relates to a power supply circuit, and in particular, to a power supply circuit having an inverting amplifier.
2. Related Art
Currently, power supply circuits are used in various electronic devices. In a power supply circuit, when a feedback is executed using a feedback-type amplifier circuit such as an inverting amplifier, a shift in phase causes oscillation, and, in some cases, an accurate output waveform cannot be obtained. In order to prevent this, phase compensation must be executed for inhibiting the shift of the phase within a certain limit range in the power supply circuit.
For example, JP 2007-188533 A discloses a voltage regulator which generates a predetermined constant voltage based on a reference voltage which is set in advance and which outputs the generated voltage from an output terminal, comprising a detecting circuit section which detects a voltage which is output from the output terminal, generates a voltage corresponding to the detected output voltage, and outputs a generated voltage, and a differential amplifier section which compares voltages between a voltage which is output from the detecting circuit section and a reference voltage, and outputs a voltage indicating a comparison result. In addition, the voltage regulator comprises a phase compensating circuit section which advances a phase of the voltage which is output from the detecting circuit section and outputs to the differential amplifier section as a feedback voltage, to execute phase compensation, an output circuit section having a driver transistor which outputs a current corresponding to a voltage which is output from the differential amplifier section and which outputs a predetermined constant voltage via an output terminal, and a phase compensation control circuit section which controls a frequency in which the phase compensating circuit section executes the phase compensation, according to the current which is output from the output circuit section.
In a power supply circuit which executes feedback of a feedback voltage using a feedback-type amplifier circuit such as an inverting amplifier, phase compensation can be executed using a phase compensating capacitor. However, when the power supply circuit has the differential amplifier which compares the reference voltage and the feedback voltage, if a capacitance value of the phase compensating capacitor is adjusted, a shift in the differential balance of the differential amplifier with respect to the change of the input power supply voltage becomes significant, and there is a possibility that the ripple removing rate may be degraded at a certain frequency region.